1. Field of the Invention
The present invention relates to a method of transmitting and receiving data, and more particularly, to a method of communicating data in a wireless mobile communication system.
2. Discussion of the Related Art
In a broadband wireless access system, a mobile subscriber station (MSS) is permitted to enter idle-mode to save power. The MSS in idle-mode does not need to perform handover procedure when moving between base stations of a same paging zone. Normally, performing handover requires the MSS to transmit in the uplink direction during idle-mode. As a result of the MSS not having to transmit to the base station (BS), power can be saved.
A MSS is located in a paging group, comprised of a plurality of base stations. The coverage area which is covered by the paging group called a paging zone. The base stations of the paging group in the paging zone share the same paging cycle and paging offset values.
The MSS transmits a request message to the BS requesting to enter idle-mode. The BS then sends a response message granting the MSS to enter idle-mode. In the response message, the BS includes paging group identification, paging cycle value, and paging offset value. The request can be made using a de-registration request (DREG-REQ) message.
In response to the request, the BS provides a response message to grant the MSS to enter idle-mode. The response message includes paging group identification, paging cycle, and paging offset of the BS. The response can be made using a de-registration command (DREG-CMD) message.
In addition, the BS provides a medium access control (MAC) address of the MSS entering idle-mode to other BSs of the paging group so that the MSS can receive paging messages during idle-mode.
During idle-mode, the BS broadcasts at specified time intervals (also referred to paging cycle) a message, inquiring whether the MSS wishes to remain in or terminate idle-mode or whether the MSS has to perform ranging operation. At the same time, the BS can transmit a paging message to notify the MSS that there is downlink data for the MSS.
Idle-mode can be terminated by either the MSS or the BS. If the MSS has to transmit data in the uplink direction, the MSS can terminate idle-mode anytime. On the other hand, if there is downlink traffic from the BS, the BS notifies the MSS to terminate idle-mode via a paging message so that the MSS can receive data. Furthermore, if the MSS in idle-mode fails to receive the paging message from the BS at specified time slot(s) or paging cycles for various reasons, such as moving to another paging zone, the MSS terminates idle-mode.
Here, the MSS in idle-mode can freely roam within the boundary of the paging zone without having to perform handover so long as the MSS does not have to receive any downlink traffic and/or transmit data in the uplink direction.
The MSS terminates idle-mode and re-registers/re-enters to the network and received downlink data if it is notified via a paging message that downlink traffic exists from the BS. In addition, as part of performing ranging operation, the MSS has the BS update the location of the MSS and an effective MSS information list. On the other hand, if the MSS receives a command via a paging message not to perform any operation, the MSS remains in idle-mode.
However, if the MSS has to transmit data in the uplink direction or if the MSS moves to a different paging zone, the BS in the paging group notifies other BSs in the paging group that the MSS is no longer in the same paging zone, thereby deleting the corresponding MSS from the list of MSSs in idle-mode.
If the MSS moves to another paging zone or need to transmit to the BS arises during idle-mode, the corresponding MSS terminates idle-mode and has to register with the new BS of the new paging group. In registering with the new BS, the MSS has to go through the registration process from the beginning—the same registration process as the initial registration process to the previous network. Therefore, the MSS expands much power to register with the new network, and at the same time, much time is spent to go through the registration process.
In addition, if the MSS wishes to retain the idle-mode information of the previous paging group after moving to a new paging group, the MSS has to request idle-mode via a MAC control message after registering with the new network. Thereafter, the BS of the new paging group provides a response to the idle-mode request. Again, such procedure causes increase in MAC signaling, thereby increasing use of power.
FIG. 1 illustrates the MSS terminating idle-mode and returning to normal mode to receive downlink traffic. Here, the MSS entered idle-mode per a request made by the MSS to enter idle-mode. In addition, even if the MSS entered idle-mode per a command from the BS, the MSS terminates idle-mode and returns to normal mode to receive downlink traffic.
Referring to FIG. 1, the MSS de-registers with a BS (BS1—host BS) via the DREG-REQ and DREG-CMD (S10). After the MSS enters idle-mode, the host BS notifies other BSs in the same paging group via paging announcement that the MSS has entered idle-mode (S11). In the paging announcement, the host BS includes a medium access control (MAC) address of the MSS. Each BS receiving the paging announcement registers the MAC address of the MSS in its paging list. This paging list is shared by all the BSs in the paging zone.
While in idle-mode, data could be sent to the MSS. In order to receive this data, the MSS must exit idle-mode. Hence, when downlink traffic exists, the host BS transmits a paging announcement to notify all the BSs in the paging group that data has to be delivered to the MSS (S12). Accordingly, each BS transmits a paging message to the MSS using the MAC address provided from the host BS during paging intervals (S13).
The MSS receives the paging message from each BSs of the paging group. If an Action Code received from one of the BSs, i.e., BS#3, is set to “10, ” which indicates initial network entry, the MSS performs ranging operation and initial network entry procedures with BS#3 (S14 and S15). Here, the ranging operation includes a ranging request (RNG-REQ) message from the MSS and a ranging response (RNG-RSP) message from the BS. After the MSS gains initial network entry, BS#3 transmits the downlink data to the MSS (S16).
Saving power is not limited to idle-mode. As another means of saving power besides idle-mode, the MSS can enter sleep mode to save power. For the MSS to enter sleep mode, the MSS transmits a request to enter sleep mode via a sleep request (MOB-SLP-REQ) message to the BS. The BS then sends a response message granting the MSS to enter sleep mode via a sleep response (MOB-SLP-RSP) message. The MOB-SLP-REQ and MOB-SLP-RSP messages includes various information such as the starting time of sleep mode, maximum/minimum sleeping interval (in frames), and listening interval(s).
At the end of the sleeping interval, the BS transmits a traffic indication (MOB-TRF-IND) message to notify the MSS of whether any downlink traffic exists. If there is no downlink traffic for the MSS to receive, the MSS can return to sleep mode. If, however, there is downlink data, the MSS returns to normal mode to receive downlink data.
FIG. 2 illustrates the MSS terminating sleep mode and returning to normal mode to receive downlink traffic. Here, the MSS entered sleep mode per a request made by the MSS to enter sleep mode. In addition, even if the MSS entered idle-mode per a command from the BS, the MSS terminates idle-mode and returns to normal mode to receive downlink traffic.
Referring to FIG. 2, the MSS transmits a request to enter sleep mode via the MOB-SLP-REQ message to the BS (S2-0). In response, the BS transmits the MOB-SLP-RSP message to the MSS (S2-1). In the MOB-SLP-RSP message, information such as the starting time of sleep mode (M), maximum/minimum sleeping interval (N1, N2), and listening interval (L1) are included.
The MSS enters sleep mode according to the minimum sleeping interval (N1) set in S20 and S21, and the BS transmits the MOB-TRF-IND message during the listening interval L1 (S2-2). It is through the MOB-TRF-IND message that the BS indicates the MSS whether there is any data to receive for the MSS (negative/positive). In addition, the MSS listens or wakes up from sleeping during L1 to check whether any downlink data exists. If there is no downlink data, which is indicated by ‘negative indication,’ the MSS returns to sleep mode. However, after a listening interval, the sleeping interval or sleeping window size is doubled according to a scheduled sleep window setting method.
If the BS receives data to transmit to the MSS during the sleeping interval, the BS stores the data in a specified storage space and waits until the next listening interval, at which time the MSS is notified of the data via the MOB-TRF-IND message (S2-3). Thereafter, the MSS wakes up from sleep mode and returns to normal mode in order to receive data (S2-4).
In normal mode, if an internet protocol (IP) packet (data) is received by the MSS, a router transmits the IP packet to the MSS via a base station. In version 4 of IP (IPv4), the router uses an ARP, and in version 6 of IP (IPv6), the router uses neighbor discovery (ND). In other words, when transmitting the IP packet to the MSS, the router uses the ARP and ND protocols to find out a target link-layer address (e.g., MAC address or Ethernet address) corresponding to the IP address of the MSS. The ARP is IPv4 protocol which is used when changing the IP address to the link-layer address, such as the MAC address or Ethernet address.
Furthermore, the ND protocol is IPv6 address used to determine the link-layer addresses of neighboring links. The changing of address occurs at the time when the IP packet header and the link-layer address header are generated. As such, the address change occurs only in the outputted IP packet.
Traditionally, it is not clearly specified as to how the BS transmits or broadcasts the request or neighboring solicitation to the MSS. More specifically, the specific role or operation by the BS has not been clearly defined in transmitting the request/neighboring solicitation to the MSS during normal mode.
Furthermore, the MSS in either sleep mode or idle-mode only receives signal at specified intervals/cycles. As a result, if the router has to transmit a received data to the MSS, a problem arises when the MSS is in sleep mode or idle-mode since the MSS cannot respond to the ARP request or neighboring solicitation until the scheduled time. Consequently, the target MSS cannot send a response, resulting in delivery failure. Based on the problem, it is possible that the MSS does not receive the data.
As discussed above, the problem exists in delivering data to the MSS from the router. Especially since in power saving sleep-mode or idle-mode of the MSS, the data received at the router cannot be received by the MSS since the MSS cannot receive until specified times. Therefore, the data is not always transmitted to the MSS.